Method of inhibiting corrosion



Patented Apr. 6, 1943 2,315,852 METHOD or ITING CORROSION Wallace E.Gordon, Wilmington, DeL, and Joseph E. Williamson, Strati'ord, Conn.,assignors to Remington Arms Company, Inc., a corporation of Delaware NoDrawing. Application June 12, 1940, Serial No. 340,088

4 Claims. (Cl. 117-127) .The invention relates to a method and materialsfor preventing corrosion of metal, particularly ferrous metals, althoughmetals not containing iron may also be protected. It also relates to amethod and materials for cleaning of metal objects, for example, thosein the process,

of-manufacture, and then preventing the corrosion of said metal objects.v

The manufacture of pocket knives can be cited as one example of a usefor the invention, although it is to be understood that the invention issuitable for any purpose wherein it is desirable to prevent corrosion.Dirt and grease accumulate on a pocket knife during manufacture,particularly from the grinding operations, and it is necessary that thisdirt be completely removedand that corrosion or rusting be preventedthereafter.- It is evident, however, that the same problem exists in amultitude of processes and manufactures and that the necessity of rustor corrosion prevention exists in a wide variety of places in whichmetals are used or processed.

The atmosphere has a particularly deleterious effect on some metals,such as those containing iron, and this is accentuated in the presenceof high humidity.

It has been found that the dirt and grease can be removed by the use ofan emulsified solvent mixture without scrubbing the article, theemulsified solvent mixture-being subsequently removed by the use of asuitable spray device. If the spray isnot used, scrubbing is necessaryif the article is very dirty. A conventional soap solution may also beused. The solvent mixture employed may comprise: a solvent for thegreaseor oil; a soap preferably of a kind soluble readily in cold water; asolvent agent for the grease solvent and the soap; and water. Oneexample of a suitable emulsified solvent mixture is disclosed in thepatent to Johnson, No. 2,032,174, wherein the preferred embodiment isdescribed as being composed of: kerosene; soap made from oleic acid andpotash; a cresylic acid as a blending agent; and water. It is to beunderstood, however, that any suitable emulsified solvent mixture may beused.

After the dirt and grease or oil have been removed, the surface of themetal is left in a clean, but unprotected condition, which will rapidlycorrode or rust. Surfaces, which are exposed to the atmosphere, have hadcoatings or materials such as lacquers and paints placed thereon toexclude .the atmosphere, the eflicacy of these coatings depending uponthe imperviousness thereof. Such a treatment of the metal by coating isnot desirable in many instances because the object is worked on ortreated after the cleaning. This is the case with the pocket knife abovementioned.

It has been found that certain inorganic nitrites, such as the nitritesof the alkali metals, when placed in contact with a metal body,Darticularly one of ferrous metal, have a passivating,corrosion-preventing action thereon. A plausible theoretical explanationis that the nitrite ion equi-potentializes the whole surface of themetal. The term alkali metal nitrite includes ammonium nitrite and is tobe so construed.

It is to be understood that where the term ferrous is used in thespecification and claims that it is intended to include metalscontaining a substantial amount of iron which is subject to rusting, andthat the term ferrous is not to be construed as limited to a metal thatis composed almost entirely of iron. a

In applying such a solution to a bright surface or to a surfacecontaining a slight film of oil or grease, the surface tension of thesolution tends to prevent the complete covering'of the surface. In orderto overcome this, it has been found that if the inorganic nitritesolution be placed in a solution having a wetting agent or agent reduc-'ing the surface tension in the solution, that the action of the nitriteis improved.

In general, wetting agents are composed of a hydrocarbon chain ofvarying length, which is more or less hydrophobic in character,depending upon the length of the chain, and has one or more groups ofstrongly hydrpphilic nature,

which act as solubilizing groups for the compound. The theory that maybe advanced is that hydrophobic matter attracts the hydrophobic part'ofthe hydrocarbon chain, and that the hydrophilic portion is' free toattach itself to any sumciently hydrophilio substance. The surfacetension of the liquid is probably reduced by the action of. the wettingagent, allowing and facilit t t Sp ad g of the solution and completenessof contact with the object.

A detergent and a wetting agent are closely ganic nitrite inhibitor overthe entire surface and into intimate contact therewith, creating thedesired passivating action.

The reduction of lathering and sudsing obtained with the compositions ofthis invention as compared with ordinary soap is important as the lathertends to get into the comers of the article, preventing adequateinspection. Another important factor is the reduction of the slipperyfilm deposited on articles by the ordinary soaps.

The emulsified solvent mixture previously described requires very littlescrubbing and, by washing thereafter, practically all of the dirt andoil or grease are removed with very little sudsing or latheringinvolved.

As a wetting agent, one of the ordinary soaps, such as the alkalinesalts of palxnitic, stearic and oleic acid may be used. Such a soap inan aqueous solution reduces the surface tension of the liquid and causesthe surface of the object to be treated to be wet thereby. It is alsopossible that the soap serves as a detergent and removes the oil or dirtfilm from the surface so that the inhibitor has access to the surface.

One of the synthetic detergents or wetting agents may be used in placeof soap. Many of the fatty alkyl' sulphates are suitable for thispurpose, the alkyl sulphate being carried in a solvent.

The following composition has been found to The bomeol terpene comprisesa solvent for the sodium oleyl sulphate, and in addition assists in thewetting action. Borneol terpene is a mixture of hydrocarbons obtained asa by-product in the isolation of terpin hydrate and camphene fromturpentine, the hydrocarbon mixture containing dipentene as the majorconstituent. The

' ethyl alcohol serves as a stabilizing solvent.

, There are other satisfactory detergent and wetting agents, such as onehaving the composition:

Per cent by weight Sodium lauryl sulphate 4.7- 5.3 Water 12.8-12.3Borneol terpene 73.3 Ethyl alcohol 3,3

. Octyl alc 5.8

The octyl alcohol comprises one of the solven and assists in the wettingaction.

Still another satisfactory wetting agent is composed of:

in aqueous solutions of relatively low concentration. It has been foundthat in the case of the sodium oleyl sulphate composition that 1% isadequate, and that for the C-cetyl betaine composition, that .5% isadequate.

In such an aqueous solution, there is placed about .1% to 3% by weightof sodium nitrite. A corresponding percentage may be used of other ofthe inorganic nitrites such as calcium nitrite.

It is possible to first apply the detergent or soap to the article andthen to dip it into the aqueous alkali metal or inorganic nitritesolution, but it has been found that the corrosion inhibition is betterwhen the nitrite is placed in a solution with the wetting agent ordetergent.

Examples of a complete method of washing and inhibiting will now begiven.

Example I The articles bearing dirt, grease and oil incident to theirfabrication are first placed in the emulsified solvent mixture bath'ofthe character described, the bath being at about 120-140 F., Thearticles are then removed and subjected to a water spray which removesthe emulsified grease and dirt. The articles are then dipped into anaqueous solution containing approximately .1% to 3% by weight sodiumnitrite and 1% by weight wetting and/or detergent agent of thecomposition comprising:

' Per cent by weight Sodium oleyl sulphate 13.5-15.0 Water 36.5-35.0Borneol terpene 40.0 Ethyl alcohol 10.0

and then allowed to dry.

Example -II The articles bearing dirt, grease and oil are first placedin the emulsified solvent mixture bath of the character described, thebath being at about 120-140" F.. and are kept there for about twominutes. The articles are then removed and subjected to a water spraywhich removes the emulsified grease and dirt. The articles are thendipped into an aqueous solution containing approximately .1% to 3% byweight of sodium nitrite with approximately .5% wetting or detergentagent comprising sodium oleyl sulphate in a Y borneol terpene and ethylalcohol solvent;

Per cent by weight Sodium lauryl sulphate 30 I Water 33 Ethyl alcnhnl18.5 Methyl cyolnhexannl Among the other agents that would be effectiveare agents containing 25% by weight of C-cetyl betaine, mixtures ofsoaps, sulphonated castor oils, and other synthetic detergents withsolvents such as tetra hydro-naphthalene, cyclohexanol and pine oil.These agents usually contain water and, in some instances, othersolvents as stabilizing agents.

The foregoing compositions are preferably used Example III The articlesare first scrubbed in the emulsified solvent mixture similar to that ofExample 1, dipped in water to wash oil. the emulsified grease and oil,then dipped into the inhibitor and wetting and/or detergent solutions ofExamples I and II and allowed to dry. The water dip is not an essentialpart of the process, but such a dip prevents the accumulation of theemulsified oil and grease in the inhibitor and wetting and/or detergentagent solution.

Example IV The article is dipped directly into the inhibitor and wettingand/or detergent agent solution described in Examples I and II.

Example V The article is dipped into a soap and water mixture,,thenwashed, and then dipped into an aqueous solution similar to that ofExample I.

It is to be understood that in the above-cited examples, the temperatureof the emulsified solvent mixture and the time of immersion therein maybe varied as desired andthat the particular nitrite or corrosioninhibitor may be any of those disclosed in the foregoing and that theamount used may be varied. The wetting agent employed may be anygofthose disclosed in this specification and the percentage varied as foundnecessary to obtain complete wetting of the surface.

The invention, therefore, is seen to disclose a simple and emcient meansof cleaning articles and rendering them corrosion-resistant to ordinaryatmospheric conditions.

It is evident that the invention permits of numerous modifications; asfor example, the concentration of the nitrite and wetting agentsdisclosed herein may be varied to obtain the best results, suchvariation being made without departing from the scope or spirit of thedisclosed invention.

What is claimed is:

l. The method of imparting corrosion resistance to a ferrous metal bodycomprising treating said body by subjecting the surface thereof to anaqueous solution consisting of an inorganic nitrite, water and a wettingagent comprising sodium lauryl sulphate, borneol terpene and an alcohol;and thereafter removing the solvent by drying said body.

2. The method of imparting corrosion resistance to a ferrous metal bodycomprising treating said body by subjecting the surface thereof to anaqueous solution consisting of an inorganic nitrite, water and a wettingagent comprising sodium oleyl sulphate, water, borneol terpene and analcohol; and thereafter removing the solvent by drying said body.

3. The method of imparting corrosion resistance to a ferrous metal bodycomprising treating said body by subjecting the surface thereof to anaqueous solution consisting of sodium nitrite, water and a wetting agentcomposed substantially of v Per cent by weight Sodium oleyl sulphate13.5-15.0 Water 36.5-35.0 Bomeol terpene 40 Ethyl alcohol 10 andthereafter removing the solvent by drying said body.

4. The method of imparting corrosion resistance to a ferrous metal bodycomprising treating said body by subjecting the surface thereof to anaqueous solution consisting of an inorganic nitrite, water and a wettingagent selected from the group consisting of sodium oleyl sulphate,sodium lauryl sulphate, alkali metal salts of palmitic, stearic andoleic acid, C-cetyl betaine and sulphonated castor oil; and thereafterremoving the solvent by drying said body.

